Teach the native viewport service to draw a Surface into itself

mojo/services/public/interfaces/native_viewport/native_viewport.mojom

Index: mojo/services/public/interfaces/native_viewport/native_viewport.mojom
diff --git a/mojo/services/public/interfaces/native_viewport/native_viewport.mojom b/mojo/services/public/interfaces/native_viewport/native_viewport.mojom
index f630031c7b3ab8f2140acdc32410e9e17c481c67..dd04f5cb17dcc927bbd3a4a06dcbc661e7963f4b 100644
--- a/mojo/services/public/interfaces/native_viewport/native_viewport.mojom
+++ b/mojo/services/public/interfaces/native_viewport/native_viewport.mojom
@@ -5,23 +5,25 @@
 import "mojo/services/gles2/command_buffer.mojom"
 import "mojo/services/public/interfaces/geometry/geometry.mojom"
 import "mojo/services/public/interfaces/input_events/input_events.mojom"
+import "mojo/services/public/interfaces/surfaces/surface_id.mojom"
 
 module mojo {
 
 [Client=NativeViewportClient]
 interface NativeViewport {
-  Create(Rect? bounds);
+  Create(Rect bounds);
   Show();
   Hide();
   Close();
-  SetBounds(Rect? bounds);
+  SetBounds(Rect bounds);
+  SubmittedFrame(SurfaceId surface_id);
 };
 
 interface NativeViewportClient {
   OnCreated(uint64 native_viewport_id);
-  OnBoundsChanged(Rect? bounds);
+  OnBoundsChanged(Rect bounds);
   OnDestroyed();
-  OnEvent(Event? event) => ();
+  OnEvent(Event event) => ();
 };
 
 }